Metallic carbides are very hard materials. They are used as abrasives, as the cutting part of lathe tools, masonry drills and the like, and as additives which increase the strength and hardness of metals and alloys used as cutting tools.
The conventional preparation of carbide bodies involves the steps of
(a) mixing a powder (preferably formed chemically, in the colloidal form) of a metal or a mixture of metals, the carbide of which is to be formed, with graphite powder in stoichiometric quantities to produce the required carbide or carbides, and optionally including an additive in the powder mixture to act as a bonding agent (for example, a quantity of powdered colbalt may be added to facilitate the bonding of the powder particles, particularly if a mixture of metal carbides is to be produced); PA1 (b) compressing the powder mixture in a mould or die to form a "green" product; and PA1 (c) sintering the "green" product at a temperature which enables the bonding between the powder particles to be effected, to form the carbide body. PA1 (a) mixing a powder of the metal with graphite powder in substantially stoichiometric quantities for the metal carbide; PA1 (b) milling the powder mixture in a ball mill or the like until a nanostructural mixture is produced, said nanostructural mixture consisting of regions of carbon and regions of the metal or a metal based solid solution, with single atoms of the metal carbide at the interface between the regions of carbon and metal or metal based solid solution, said regions having an extent of from about 3 nanometers to about 100 nanometers; PA1 (c) moulding the nanostructural mixture to produce a moulded body; and PA1 (d) heating the moulded body to a temperature sufficient to cause (i) a solid state reaction between the carbon and the metal, and (ii) sintering of the moulded mixture, thereby producing a solid body of the metal carbide. PA1 (a) mixing a powder of the metal with graphite powder in substantially stoichiometric quantities for the metal carbide; PA1 (b) milling the mixed powder in a ball mill or the like until a nanostructural mixture is produced, said nanostructural mixture consisting of regions of carbon and regions of the metal or a metal based solid solution, with single atoms of the metal carbide at the interface between the regions of carbon and metal or metal based solid solution, said regions having an extent of from about 3 nanometers to about 100 nanometers; PA1 (c) mixing said nanostructural mixture with a powder of the metal in proportions corresponding to a pre-determined ratio of dispersed phase and matrix phase in the composite body; PA1 (d) moulding said mixture of the nanostructural mixture and metal powder to form a moulded body; and PA1 (e) heating the moulded body to a temperature sufficient to cause (i) a solid state reaction to form the metal carbide, and (ii) sintering of the moulded body, thereby producing said composite. PA1 (a) mixing a powder of the metal with an organic surfactant in proportions such that the carbon content of the surfactant provides substantially the stoichiometric quantity of carbon to form the metal carbide; PA1 (b) ball milling the mixture of powder and surfactant to produce a nanostructural mixture comprising crystals of the metal, or of a metal based solid solution, dispersed within a matrix consisting of metal atoms, carbon atoms and hydrogen atoms, the metal or solid solution crystals having a diameter of the order of 10 nanometers; P1 (c) moulding the nanostructural mixture to form a moulded body; and PA1 (d) heating the moulded body to a temperature sufficient to cause (i) a solid state reaction between the metal and the carbon in the moulded body, (ii) release of the hydrogen as a gas, and (iii) sintering of the moulded body, to thereby produce a body of the metal carbide.
It has been suggested previously that carbides can be produced by mechanical alloying. For example, the production of carbides of transition metals and elements of groups IIIA and IVA of the periodic table, using a mechanical alloying technique, has been described in the specification of International patent application No PCT/FR89/00384 (World Intellectual Property Organisation publication No WO 90/01016). The examples given in that specification show that when a small quantity of a powder of an element of the specified group is milled with graphite powder for around 24 hours in an inert atmosphere (usually argon), a carbide of the element is produced. In general, the carbide produced is that which would be expected from a complete reaction of a stoichiometric mixture of the element and graphite, but in some instances (for example, when the element is niobium, molybdenum or vanadium), "new" carbides are formed. However, the carbides formed by this technique (which is also reported in the paper by P Matteazze, G Le Caer and E Bauer-Grosse entitled "Synthesis of Advanced Ceramics by High Energy Milling") are deduced to be present from the analysis of X-ray diffraction patterns of the product powders and there appears to have been no attempt to form dense ceramic bodies from the small volume samples of the product carbides that are shown to be present. Certainly there is no indication that it would be possible to form machine tools or the like from carbide powders produced by the mechanical alloying process.